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If you choose the wrong n, you'll still get blob of random data back, just not the correct one.

Now, the tricky part is in making sure the incorrect keys returns data that's hard to distinguish (meaning it can't be done automatically and/or quickly) from the correct plain text, when the plain text ISN'T random looking, but something like passwords, SSN, credit card numbers.

If one has the ability to back up that risk, (...) it is on average better to not get insurance.

I don't get why this concept is so hard for people to understand.

Like people taking out insurance for canceling a holiday trip. If you have paid up front for your vacation, then pretty much by definition you can afford to lose that money without ill effects worse than "I won't get to go on holiday this time"

JoeMerchant was implying his crypto method was perfectly safe against cryptanalysis because it's a one-time pad. However, in the same post he tells us he's not using a one-time pad at all, but a stream cipher.

You just told all of us your method, and we didn't even need to use a wrench.

One time pads are only unbreakable when they're generated with a true random source. What you described is a stream cipher, and as long as you know the key to initialize the keystream, it can be forced from you.

Of course, if you do have a true one-time pad, the location of your copy of it can be extracted just as easily. I'd say the only way to protect against that is to make sure no-one knows you use crypto at all.

They're exactly the same as the casino owner: the house always gets its cut.

Not quite. The casino sets the rules of the game, making sure they know EXACTLY what the odds are, thereby turning long-term profit into a statistical certainty. The insurer has to guess the odds, and can actually guess wrong, so there's a lot less certainty. That's why there are reinsurers, who insure the insurers against unexpectedly large payouts.